Limit of Number of domains is set to 0, but the webspace (and domain of the same name) still could be created.
- The value of Number of domains limits the amount of domain in each webspace. It means it can be exceeded the more times the more webspaces exist in subscription.
The behavior was considered as internal software issue with id #PPA-2109 that was fixed in PA 11.5 MU#11.
In order to fix the issue please install update 11 as described in the article.